Large jugs? Sorry...was expecting to see something different here. lol

Really don't know why you couldn't go with the larger displacement jug. I think the lower ends are basicly the same on most all the china girls and I would assume the cranks the same, but perhaps more research is in order

There are a lot of modifications that will increase speed, porting done right is one. Adding a expansion chamber is another, changing rear sprockets from a stock 44t to something with less teeth will increase top speed but cuts hill climbing ability. If you do upgrades do one thing at a time, that way you'll know if what you did helped or hurt performance.

Mouse, getting a bike to do those speeds is not a problem. Doing those speeds safely is the real issue. You are asking for motorcycle performance from a bicycle, so that bike and all of it's components must be up to the task. I'm guessing that about 75% of your budget and efforts should go into building a solid bicycle foundation to bring it up to manufactured moped standards.